You will need 2 equations, since there are 2 variables (hours worked by George and the ones of Dorothy), let's say x and y respectively
We know x+y=48 (since they work 48 hours together) and 12x+11.25y=555 (since the sum of their respective hours multiplied by their salary gives a total of 555$)
To solve that, you can isolate either one of the variables and replace it in the second formula, for example:
x+y=48, therefore x=(48-y) <span>Substitute x in 12x+11.25y=555 and solve for y (to find Dorothy's hours) </span><span>12(48-y)+11.25y=555 </span>576-12y+11.25y=555 21=0.75y y=28